Hybrid vehicles have an electric drive (EV) mode, in which the hybrid vehicle travels only by power from the motor-generator, and a hybrid drive (HEV) mode, in which the hybrid vehicle can travel by power from both the engine and the motor-generator. Hitherto, various types of hybrid driving devices used in hybrid vehicles have been proposed.
Japanese Patent Application Publication No. 11-082260 shows one type of such a hybrid drive system. The hybrid drive system disclosed therein includes a motor-generator disposed between an engine and a transmission as a result of connecting an output shaft of the engine and an input shaft of the transmission. A first clutch connects the engine to the motor-generator so that they can be separated from each other. A second clutch connects an output shaft of the transmission and the motor-generator so that they can be separated from each other.
When the first clutch is disengaged, and the second clutch is engaged, the hybrid vehicle including the hybrid driving device is put in the electric drive (EV) mode, in which the hybrid vehicle travels only by power from the motor-generator. When the first and second clutches are both engaged, the hybrid vehicle including the hybrid driving device is put in the hybrid drive (HEV) mode, in which the hybrid vehicle can travel by power from both the engine and the motor-generator.